On 23 January 2020, a Cessna S550 (ZS-CAR) being operated by the Flight Inspection Unit (FIU) of the South Africa Civil Aviation Authority for instrument approach calibration flights departed George, which is at an altitude of 648 feet amsl, on a day VFR flight plan in order to make a series of calibration flights in respect of the runway 11 ILS at George. As it levelled off downwind at 3,900 feet QNH, almost 1000 feet higher than originally advised, radar contact was lost and only a single MAYDAY call was heard a few seconds later. The wreckage was subsequently located in mountainous terrain at 2,200 feet amsl with no survivors.
Because the accident had occurred to an aircraft operated by the South African CAA, a formal request in accordance with the corresponding provisions of Annex 13 was made to the Ethiopian Accident Investigation Bureau (AAIB) to perform the necessary Investigation rather than have it performed by the South African CAA Accident and Incident Investigation Division (AIID). This request was accepted and a formal agreement was made on 25 January 2021 under which the Ethiopian AAIB would complete an Investigation and submit the final draft report to the AIID for comment. When the two parties are agreed, the final report would be publicly released by the South African AIID.
The FDR was recovered in an externally damaged state but, whilst some relevant data was successfully downloaded from it by the French BEA, only 7 of the 16 parameters for which recording was mandatory under the State Civil Aviation Regulations (CARs) were found to have been recorded. The aircraft did not have a CVR installed and was not required to have one.
The Flight Crew
It was noted that the 49 year-old Captain, who was the Chief Pilot of the Flight Inspection Unit and simultaneously a CAA Operations Officer, had a total of 5,215 hours flying experience including 1,315 hours on type of which 15 hours had been recorded during the previous 90 days as the only hours flown on any aircraft type. He had previously completed approximately 20 hours of flight calibration work at George. On examination of the record of the Captain’s six monthly proficiency checks, it was found that his last Pilot Proficiency Check (PPC) was on 31 May 2019 and was therefore valid only until 30 November 2019 indicating that it had therefore “expired before the accident”. However, it was seen that he had attended the ‘FlightSafety Textron Aviation Training’ in San Antonio USA on 8 November 2019. Whilst there, he had completed training on PPC items which had included a corresponding certificate confirming this but without any endorsement that he had reached the necessary performance standard in those items for issue of a PPC. No such certificate was provided and it was found that instead “the current training document submitted by the South African CAA showed that the Captain had conducted a PPC 08 Nov 2019 which would expire on 07 May 2020”.
The 33 year-old First Officer had a total of 1,061 hours flying experience of which 265 hours were on type. She had previously completed 2 hours of flight calibration work at George and, paired with the same Captain, had completed approximately 200 hours of flight calibration duties comprised of 58 VOR and 50 ILS calibrations.
It was noted that prior to departing on the accident flight, the aircraft, with the Flight Inspection Unit Inspector who was tasked with operating the calibration equipment on board, had positioned from Port Elizabeth and had requested clearance to carry out a calibration flight approach for the ‘GRV’ VOR at George but had not received it because of prevailing poor weather conditions. As a result, it was decided to land and refuel the aircraft before commencing the calibration of the runway 11 ILS instead.
The First Officer requested start for an ILS calibration flight climbing to 3000 feet QNH and advised an endurance of 4 hours 30 minutes which was approved. A subsequent request was made to intercept the 250° radial from the on-aerodrome ‘GRV’ VOR by turning right after a runway 11 takeoff and climbing to 3000 feet QNH to join the 17 DME clockwise arc and then follow this until reaching the 330° radial from the same VOR climbing to 4000 feet QNH (see the illustration below). This request was approved.
The aircraft was subsequently airborne at 1042 local time with the Captain acting as PF. The radar recording indicated that it had thereafter followed the approved route. The George METAR timed shortly after the takeoff gave the aerodrome surface visibility as greater than 10km and the lowest cloud there as BKN (broken) at 2400 feet aal, about 1000 feet below the intended climb to the northwest of the airport to 4000 feet QNH.
The ground track of the accident flight. [Reproduced from the Official Report]
Eight minutes after takeoff, the aircraft commenced a right turn onto the 17 DME arc and appeared to level off at 3,900 feet QNH but after about half a minute FDR data showed a wing drop without a further heading change occurring and a rapid descent of 1500 feet occurred within approximately 9 seconds during which a MAYDAY call was received. At 2,400 feet QNH, the aircraft appeared to have been beginning a recovery from the dive and three seconds prior to impact - now below higher terrain in the vicinity leading to loss of the radar target - the 32.5° nose down pitch was reduced to 17.5° at which attitude impact occurred. ATC contact calls received no response and a DETRESFA was declared. No ELT signal was received but a search and rescue operation was immediately commenced by the emergency helicopter on standby which located the accident site after about an hour.
The crash site, spread over a 270 metre radius circle, was in the Outeniqua Mountains northwest of the town of Friemersheim at an elevation of 2,192 feet. It was immediately evident that the aircraft had been destroyed on impact having approached the gently-rising slope of an east-west ridge from the south at a relatively shallow angle. FDR data was subsequently found to indicate that the last recorded airspeed was 286 knots. Neither the ELT nor the TAWS installed on the accident aircraft were recovered.
Why It Happened
The initial part of the ILS calibration task was to fly 35° on either side of the runway centre line while maintaining a 17 nm DME arc at a height of 2000 feet agl or obstacle plus 1000 feet (see the illustration below). Therefore the position of the aircraft at the time control appeared to have been lost was about the point where the aircraft would have turned towards the runway 11 threshold after completing the first 17 DME arc track.
The ILS 17 nm arc flight calibration check. [Reproduced from the Official Report]
A detailed examination of the available flight data following a sudden right turn as the aircraft was about to reach 4000 feet QNH led to the conclusion that it was indicative of a loss of control and a rapid descent from which a recovery climb was being attempted at impact. Available webcam images at the time confirmed that the peaks of the mountains northwest of the airport were in cloud at the time. There was no evidence from FDR data of any windshear.
No evidence that the Captain had completed a UPRT exercise in the simulator during his most recent training session was found and it was considered that this fact had the potential to have been significant. It was also an explicit requirement that all Flight Inspection Operations must be conducted under VFR.
An examination of maintenance documentation found that the aircraft was not being maintained in accordance with CAA regulations although this was particularly with reference to the FDR and no evidence suggesting that lack of airworthiness had contributed to the accident scenario was found.
Irregularities were found in respect of the Flight Inspection Unit’s approval as an Electronic Service Organisation (ESO) which was a CAA regulatory requirement for any provider of flight calibration services. In 2019, the ESO approval was found to have lapsed whilst calibration work continued and even when held was invalidated by the absence of an employed or contracted “compliance officer” as required under the corresponding part of the CARs.
Since there was no CVR record and the TAWS unit was not found, it was not possible to establish whether relevant TAWS annunciations had occurred.
The Probable Cause of the Accident was documented in narrative form as follows:
The crew lost control of the aircraft which resulted in significant loss of altitude; as they attempted to recover, they collided with the mountain. According to the official weather report, there was significant cloud cover below 1500 feet above ground level at the time of the accident as recorded in the METARs with mountain tops, including those which the aircraft ground track passed over were obscured as seen on the airport webcam. From the limited FDR reading the aircraft attitude drastically changed into an unusual attitude when approaching the mountainous area which indicated that, most probably, the pilot had entered into an unusual attitude during transition from VFR to IFR flight without preparation. The accident flight plan was VFR.
Four Contributory Factors were also identified as follows:
- The presence of low cloud at about 1500 feet below above ground and mountain tops obscured mountains by cloud.
- The incapability of the crew to recover from an unusual attitude; lack of effective supervision of flight operations and disregard of relevant requirements of the Civil Aviation Regulations by the Flight Inspection Unit (as the aircraft operator).
- Overbanked and steep dive manoeuvre and inability to gain the required altitude before impact.
- The lack of Upset Prevention and Recovery Training (UPRT) for Flight Inspection fight crew.
Four Safety Recommendations were made by the Ethiopian AAIB as a result of the Investigation as follows:
- that the South African CAA considers installing a CVR on aircraft flying for calibration purposes and other flights.
- that the South African CAA ensure that operators install FDR's that record all mandatory parameters as required by the regulations. (e.g. in accordance with Part 135.05.10).
- that the South African Government should establish an agency which is independent from State aviation authorities and other entities that could interfere with the conduct or objectivity of an investigation or be vulnerable to a conflict of interest.
- that the South African CAA conducts an in-depth review of FIU operations to ensure that the operator complies with applicable regulatory requirements including those requiring that flight crew are proficient in unusual attitude recovery.
The Final Report was submitted to the South African CAA AAID in final draft form on 16 November 2021 and eventually published online on 24 January 2022.